Abstract:This paper presents the preliminary study on nitrogen—fixing bacteria from the roots of Masson pine saplings．The results show that nitrogen—fixing bacteria can be isolated universally from the roots of masson pine saplings planted in six kinds of soils， but the effects of isolation among six kinds of soils were different．142 strains of the nitrogen-fixing bacteria were obtained by two methods，of which one strain A′10 is identified as Alcaligenes paradocrus．Inoculation of seeds of masson pine with twenty—six strains were done，while inoculation of nine strains were successful．Nitrogenase activity of four strains，I．E．A′10，A′13，G1 ＆ g2w，were measured，and the results are as following：A′10，2.10-3.50 mgN/g glucose；A′13，4.20-5.13 mgN/g glucose； G1，3.66-6.83 mgN/g glucose；g2w，1.93-2.60 mgN/g glucose．